I mix the 2 all the time--it works great! I got the idea from another CC'er here (can't remember who). It's a great combo: not too sweet, and smooth/creamy! IMBC can set out for 12 hours, but I'm wondering if this can be extended with the 50/50 combo because of the higher sugar content from the BC??
If you keep meringue powder on hand, there's a new recipe (posted yesterday?) that's an IMBC. I haven't tried it yet, but it sounds great!
I have to tell you, I mix one batch of IMBC (WBH, I think) and a double batch of Wilton's 50/50 BC all the time. IMBC by itself won't hold up in Florida at this time of year. I do keep it cold and direct whomever is consuming the cake that it needs to be kept cold.
I think it's especially delicious and try to not ever have leftovers because my hips are big enough already, TYVM! 
It did work! I live in the Central Valley of California and while it's not very humid, it definately gets HOT.
I was very worried about it melting. It did get VERY soft, but still held together nicely.
I found it to be a nice combo! IMBC is sooooo buttery and traditional 50/50 bc is soooooo sweet. This brought a nice balance of smooth and sweet.
Good, glad it worked for you. I tried it with a cooked French Buttercream and standard powdered sugar/crsco buttercream and it did not work well, it separated and developed large air bubbles. I had not tried it with IMBC so was hesitant to suggest that.
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